In such a blow valve known in practice, the upper side of the wall, which is opposite to and spaced from the mouths, is flat and perpendicular to the shifting direction of the valve piston. The piston extension has a flat surface which is perpendicular to the shifting direction and on which the closing surface is formed. For an easier handling of the circular closing surface the surface may comprise a central, flat and shallow recess at the end of the piston extension. The flow developing in the open position of the valve piston in the valve chamber must be deflected twice. When the blow valve is opened, the flow expands into the large-volume cylindrical valve chamber, the depth of which corresponds approximately to the opening lift and the diameter of which corresponds several times to the diameter of each mouth. The turbulent and delayed medium must squeeze out of the valve chamber into at least one mouth of the outflow channel and must be accelerated again. Dead spaces as well as considerable pressure losses caused by turbulences ensue from the geometric concept in the valve chamber, i.e. the flat surfaces oriented perpendicular to the shifting direction of the piston. It is difficult to clean the blow valve in the dead spaces. The unavoidable pressure losses result in undesired long switching differences between the opening pulse and the pressurization of the preform.
In the blow valve known from EP 1 328 396, the flow developing in the open position is deflected at least three times, each time by 90°, and expands in the large valve chamber. Strong turbulences resulting in inexpediently great pressure losses and long switching differences are created in the valve chamber.
It is one aspect of the present disclosure to indicate a blow valve of the aforementioned type which in the open opposition operates with a minimum pressure loss and thus with an optimally short switching difference. It is also part of the aspect to avoid inexpedient dead spaces that increase the compressed air consumption and deteriorate the cleanability, e.g. by way of rinsing the blow valve with a cleaning medium.
The at least one, generally inclined, guide surface effects a lateral forced deflection of the flow in the valve chamber, whereby strong turbulences caused by great pressure loss are minimized. The decrease in pressure loss is accompanied by an optimally short switching difference. Expediently, at least one guide surface is provided both in the wall and on the piston extension to create a low-turbulence, swift and, above all, guided flow from the inflow channel into the outflow channel in the open position. An improvement is however achieved with at least one guide surface on the piston extension or in the wall. Unharmonious or sharp and turbulence-promoting surface transitions are minimized. Only minimal dead spaces are created, if at all. The formation of swirls is thus minimal and the blow valve can be cleaned easily, e.g. in a rinsing process.
In an expedient embodiment, the respective guide surface, facing the flow, is concavely rounded at least in portions. A concave rounding considerably improves the flow pattern in the flow and thus reduces the pressure loss caused during deflection.
It is advantageous when the valve seat which is substantially oriented perpendicular to the shifting direction of the valve piston and/or the closing surface on the valve piston, is/are made flat, spherical or conical. Especially spherical or conical configurations that may be similar or alternate or may be combined with a flat design result in high tightness in the shut-off position, and also help to make the flow uniform, thereby further reducing the pressure loss.
In an expedient embodiment, the guide surfaces on the wall and on the piston extension harmoniously pass into one another in the open position so as to put up as little flow resistance as possible to the exterior faster boundary layer of the flow.
In an expedient embodiment the guide surface even extends on the wall directly up to the mouth, so that the flow is directly guided up and into the mouth without any significant separation.
In a constructionally simple embodiment the wall is formed by a ring stationarily inserted into the valve chamber. It may be the function of the ring to define with the bottom side a pilot chamber in which the valve piston is actuated by a closing force-generating pilot pressure on an actuation surface larger than the piston extension. Preferably, because of the larger actuation surface a relatively moderate pilot pressure suffices for holding the shut-off position and after reduction of the pilot pressure the valve piston is brought by the inflow pressure very rapidly into the open position.
In a particularly expedient embodiment, apart from a central mouth, two exterior mouths that are diametrically arranged relative to the axis of the central mouth are provided that have each assigned thereto an outwardly ascending guide surface on the wall. By contrast, the piston extension that is oriented relative to the central mouth and immerses at least in the shut-off position into the central mouth in portions comprises two descending guide surfaces that are connected via an elevated flow division zone and oriented relative to the exterior mouths. The mouths may be circular, oval or kidney-shaped, or they may have any desired shape. It would also be possible to provide just one exterior mouth. In this configuration, an especially neat flow guiding operation with a low pressure loss is achieved. Independently of the question which mouth pertains to the inflow channel and which one to the outflow channel, either the flow from the inflow channel mouth is divided with low loss into two substantially identical partial flows that are guided to the exterior mouths, or two partial flows from the exterior mouths pertaining to the inflow channel are harmoniously combined in a flow extending into the mouth to the outflow channel.
To keep dead spaces as small as possible, and to enforce a neat flow-guiding process, it may be advantageous when the guide surfaces are formed in trough-like recesses in the piston extension and in the wall. The width of each recess can here correspond to the diameter of the exterior mouth or the central mouth.
In an expedient embodiment, these recesses have at least about the same depth in the shifting direction of the valve piston, resulting in a harmonious flow path of a large cross-section in the open position.
Particularly expediently, the guide surfaces are defined by displacement bodies provided on the wall and the valve piston. The displacement bodies minimize the dead volume in the valve chamber, so that the guided flow is without any expansion generating significant pressure losses and without any swirl.
In another expedient embodiment, the recesses in the flow direction can even gradually narrow down and preferably form a nozzle cross-section similar to a venturi nozzle that is constricted towards the outflow channel, so that the flow is made uniform and accelerated, whereby the pressure loss can even be reduced further.
The flow direction in the blow valve can be chosen according to requirements. The central mouth is preferably assigned to the inflow channel and the exterior mouth or both exterior mouths are assigned to the outflow channel.
The ring arranged in the valve chamber may be split into a lower ring providing the necessary sealing and into an upper ring serving to guide the flow. The ring serving to guide the flow could also be used for retrofitting already used blow valves, and it could even consist of plastic.
To improve the flow conditions also in or from the respective mouth, at least one of the mouths may comprise a counter-guide surface.